The present invention relates to a mobile communication system including an exchange, a plurality of base stations connected to the exchange and a multiplicity of radio telephone sets belonging to the radio service areas of these base stations, and more particularly, to a system for integratedly controlling the radio service areas of the base stations in the mobile communication system.
In a conventional mobile communication system, base stations are arranged with pre-assumed traffic so that, when there occur calls exceeding the assumed traffic from radio telephone sets, the connections are limited, causing call loss. In order to cope with such peak traffic, it has been necessary to increase the number of base stations. Further, when one of the base stations becomes faulty in operation, it becomes impossible to use the radio telephone sets belonging to a radio service area so far covered by the faulty base station, so long as the faulty base station is not repaired or replaced by a normal one.
In this way, with the above prior art mobile communication system, for the purpose of relieving the traffic congestion or the call loss caused by the faulty base station, it has been necessary to increase the number of base stations by newly installing them.
Meanwhile, there is already known a system in which an telephone exchange has such a function of monitoring load states of a plurality of base stations that, when detecting an overload of specific one of the base stations, the exchange changes the transmission outputs of directional antennas of the radio base light-loaded stations other than the overloaded station to distribute the overload to the light-loaded other base stations, as shown in JP-A-3-22632. Also as disclosed in JP-A-3-117040, there is already known a system that directional antennas having a variable output level are provided to respective base stations so that an area control station calculates latent traffics of traveling equipments for the respective base stations within a fixed time on the basis of the current positions, control zone numbers and other information of the respective base stations, and adjusts outputs of the directional antennas based on the calculated result to thereby level a call loss probability. Another system is disclosed in JP-A-5-63635 in which, when the traffic of a base station becomes higher, a transmission output of an outgoing control channel of the base station is reduced to decentralize the traffic to adjacent base stations. Also disclosed in JP-A-5-259967 is a method by which a multiplicity of waiting base station for use at the time of high traffic are previously prepared for base stations always in operation so that, at the time of the high traffic, the service areas of the working base station are reduced to operate the waiting base stations.
The aforementioned, known, prior art mobile communication system has had a defect that, when it is desired to avoid traffic congestion or to prevent call loss generated by a faulty base station, the system copes with it by increasing the number of base stations to be newly installed or by individually monitoring and controlling the respective base stations, which disadvantageously results in that the overall system cannot be efficiently operated.
It is accordingly an object of the present invention to provide a system for integratedly controlling radio service areas of base stations in a mobile communication system, which can suppress call loss in an existing system facility even when traffic congestion temporarily takes place.
Another object of the present invention is to provide a system for integratedly controlling radio service areas of base stations in a mobile communication system, in which, even when one or more of base stations in the system stop their operation, the other working base stations can cover the service area or areas of the stopped base station or stations which become inactive during exchange or repair of the stopped base station or stations to thereby suppress call loss.
In accordance with the present invention, the above object is attained by providing a mobile communication system in which an exchange monitors current operation states of all base stations to manage the operation states of the base stations, compares the operation states of the base stations with a plurality of base-station state patterns previously stored in the exchange, selects suitable one of the base-station state patterns, and then issues instructions to the respective base stations to cause radio service areas of the base stations to be set to have desired radiation patterns.
In accordance with an aspect of the present invention, each of the base stations has a function of changing its radiation pattern, transmission output or reception sensitivity, that is, of setting the radiation pattern, transmission output or reception sensitivity according to the base-station control data of radiation patterns received from the exchange.
In accordance with another aspect of the present invention, when one of the base stations stops its operation due to a line fault or the like, the exchange has a function of issuing instructions to the other base stations to change their radiation patterns, transmission outputs or reception sensitivities and to cause the other base stations to cover the service area of the faulty base station.
In accordance with yet another aspect of the present invention, the exchange has a function of, when failing to search for the state pattern of one of the base stations, informing of the search failure fact and also of entering a new state pattern as necessary.
In the mobile communication system of the present invention, when any of the base stations has traffic congestion or becomes faulty, the exchange issues instructions to the respective base stations to cause the base stations to controllably change their radiation patterns, transmission outputs or sensitivities of an array antenna. In this way, since the service areas of the base stations can be suitably reconfigured, the system can effectively make the most of an existing working facility while eliminating the need for additional extending provision of a line interface circuit in the exchange and for extending works involved, thus reducing call loss.